Method for plasticizing wood

ABSTRACT

WOOD IS TREATED BY BEING INITIALLY IMPREGNATED WITH HYDRAZINE. THEREUPON WOOD IS SHAPED IN THE USUAL MANNER AND THEN EXCESS HYDRAZINE IS REMOVED. HYDRAZINE IS PREFERABLY USED IN AN AQUEOUS SOLUTION. WOOL MAY BE HEATED AFTER THE IMPREGNATION. THE PROCESS IS SUITABLE FOR TREATING WOOD VENEERS AND VARIOUS WOOD BOARDS.

United States Patent 3,788,929 METHOD FOR PLASTICIZING WOOD JoukoHuttunen, Porvoo, Finland, assignor to Neste 0y, Helsinki, Finland NoDrawing. Filed June 8, 1970, Ser. No. 44,636 Claims priority,appliiation Fginland, June 10, 1969,

Int. Cl. B27i1 1/00; C09j /02 US. Cl. 156-307 2 Claims ABSTRACT OF THEDISCLOSURE The present invention concerns a method for plasticizing woodfor the purpose of its shaping. Wood that has been treated according tothe method can be, for instance, bent and compressed and twisted withoutdamage to the wood, and thereby it acquires a new, stable shape.

It is known that the bendability of wood can be increased in some degreeby treating it with hot water or steam. After the wood has becomesaturated with moisture, it can be bent and subsequently dried underpressure. In addition to the fact that in this method prolongedtreatment periods are required, treatment with hot water or with steamcauses in the wood physical and chemical changes which impair itscharacteristics. It is also a fact that the bending accomplished withthe aid of such treatment is not particularly permanent.

According to another method, the wood is impregnated with anhydrous,liquid ammonia or aqueous solution of ammonia, whereupon the wood can bebent into desired shape, in which shape it remains after the ammonia hasbeen removed by evaporation.

The following explanation has been given for the mechanism of thisprocess. Ammonia is able to penetrate not only into the amorphousregions of the cell walls but also into the crystal structure of thecellulose and into the phenolic lignin bonding substance. Ammonia breaksup some of the hydrogen bonds which are responsible for the normalrigidity of wood. Softening of the cellular structure permits thesliding of structural components past each other under effect of anexternal force. After evaporation of the introduced ammonia, hydrogenlinkages are once more formed between the polymer chains and the woodstructure becomes re-cross-linked to its former rigidity.

A great drawback of the ammonia method is the low boiling point of theimpregnating fluid, which makes the use of refrigerating and liquefyingequipment indispensable. Moreover, ammonia is poisonous and specialprecautions are necessary for this reason.

It has now been found that ammonia, which is such an inconvenientWood-treating agent, can be replaced with hydrazine, by the aid of whichwood can be plasticized, or softened, so that it can be bent intodesired shape. In addition to bending, also considerable compression ofthe wood is rendered possible by hydrazine.

Aqueous solution of hydrazine has been found to dissolve Bjoorkmanslignin and to soften the so-called lignin-carbohydrate complex. Whenwood is impregnated with hydrazine, it thus appears obvious that in thewood occurs partial softening and solution of lignin and its dispersalin the wood substance. Furthermore, hydrazine apparently reacts withlignin, with the result of cross link- Patented Jan. 29, 1974 agesbetween lignin molecules, whereby the molecule size of lignin ismultiplied. In likeness with ammonia, hydrazine also has an eifect oncellulose.

The effect that has been discovered is employed in a method according tothe present invention for plasticizing wood for purposes of shaping, andthe invention is mainly characterized in that the wood is impregnatedwith hydrazine and that subsequent to shaping the excess hydrazine isremoved.

The hydrazine may be pure or in the form of a solution, e.g. an aqueoussolution. Of course, other solvents or vehicles appropriate for thepurpose are equally usable. The essential thing is that the impregnatingfluid contains hydrazine in sufiicient amount. It is thus possible touse hydrazine solutions which have concentrations between 1 and percent,most appropriately 3-15%. It should be noted that the wood to be treatedmay also be green timber, provided that more concentrated hydrazinesolution is then used.

For the purpose of impregnating the wood with hydrazine any suitableimpregnating method may be used. As a rule, in such methods variouscombinations of vacuum and pressure treatments are employed.Impregnation is suitably effected e.g. in a pressure vessl, in which atfirst a vacuum is created in order to draw the air from the pores.Hydrazine solution is then admitted into the vessel and allowed to beabsorbed, possibly at first under vacuum, and then at normal pressureand/or over-pressure. Impregnation may also be effected by means ofbrush application.

In the impregnation treatment the wood becomes pliable and soft. Theplasticity may be further increased by means of a fairly short, e.g.10-30 minutes, heat treatment (at 80-100 C.). Subsequent to impregnationthe wood can be bent and/or compressed. The bendability of the woodafter impregnation is very remarkable indeed. For instance, pieces ofbirch wood 20 mm. in thickness (with longitudinal direction of grain)can be easily bent by hand into an arc of 180 degrees with about 3 cm.bending radius, Without inflicting any damage to the wood. After thehydrazine has been evaporated, the wood retains the bent shape andsubsequently resists bending considerably more strongly than untreatedwood.

It is also possible after impregnation to compress the wood, wherebyfrom it escapes hydrazine solution in which lignin has been solved. Witha common manually operated screw press, the volume of the wood can beeasily reduced by more than 50% in the direction perpendicular to thegrain. After or during compression the volatile substances may beremoved by means of heat treatment, whereby the wood acquires a new,stable shape and considerably altered characteristics.

Compression is most appropriately accomplished during heat treatment.The pressing temperature may be, for instance, l00200 C., suitably C.The pressing and drying time may vary, depending on the desired finalresult, wood species, dimensions, pressing temperature, etc. As a ruleabout 4 hours pressing and drying time is sufficient. During thepressing and drying treatment mainly hydrazine evaporates from the woodand can be recovered by condensation. Measurements of the nitrogencontent of the wood after treatment have revealed that hydrazine remainsin the wood in the amount of about 2% referred to the dry weight of thewood.

Then density (volume weight) of the wood increases considerably as aresult of compression. As a rule, the density of hardwoods increasesmore strongly than that of softwoods.

Another consequence of the compression and heat treatment isconsiderable increase in hardness of the wood. For instance, thehardness of birch wood in untreated condition, and measuredperpendicular to the grain, is about 200 Brinell degrees, but woodtreated according to the present invention may present with acorresponding Brinell hardness higher than 2000. The hardness measuredin the direction of the grain is even higher, and it may be up to about3000 Brinell degrees.

It has further been noted that treatment according to the inventionimproves the dimensional stability of the wood. The dimensions changemore slowly and in lesser amount in humid air than those of untreatedwood. Submerged in water, wood according to the invention swells equallyas untreated wood, though at a slower rate, but on drying it largelyregains its improved hardness and strength. Also, it does not check inthe course of drying upon water immersion.

Hydrazine impregnation and subsequent pressing and heat treatment has,as a rule, a darkening effect on the color of the wood. The change incolor depends on the heating temperature and heating period employed.The color of birch becomes brown, that of alder becomes rcddish brown,while pine only begins to darken after prolonged heating. It is thuspossible, by varying the heating periods and temperatures, to achievecolor shades simulating valuable wood species in common wood.

The wood species has not been found to impose any restrictions onapplication of a method according to the invention. Good results arethus achieved with hardwoods as well as softwoods.

Wood treated by a method according to the invention may be used toadvantage e.g. in the furniture, ski, packing case and boat industriesand on the whole in any applications where bending of wood comes intoquestion. It may also be employed in any such instances of use in whichthe natural hardness or strength of wood does not suffice. An importantfiield of application is that of the board industry, in which woodboards or veneers treated according to the method in hand may be gluedonto various board materials, such as plywoods, stave boards, fibreboards, chip boards, etc. It goes without saying that the pressing anddrying procedure of the veneers and gluing of the laminated product maybe combined in one work phase. It is also possible to apply on thetreated wood material an appropriate coating, e.g. a paint or lacquercoat.

The fluid which runs oif when hydrazine-impregnated wood is incompression can be recovered and, if desired, reused for theimpregnation of wood. From this fluid the lignin may possibly beseparated by precipitation, for instance, and the dilute hydrazine thusobtained may be made up with fresh, concentrated hydrazine. It islikewise possible to recover the hydrazine evaporated in the heattreatment and to reuse it for impregnation.

The method according to the present invention is now illustrated by thefollowing, non-restrictive examples, which disclose some of itsembodiments.

EXAMPLE 1 A piece of room-dry birch wood (moisture content 6-7%) havingthe dimensions 20.4 mm. x 62.3 mm. x 580 mm. was impregnated with 15%aqueous solution of hydrazine as follows. The piece of wood was firstplaced in a pressure cylinder, which was evacuated so that the pressurebecame less than mm. Hg. The hydrazine solution was then admitted intothe cylinder and allowed to be absorbed under normal pressure for 15minutes. The pressure was then raised to be 5 kg./cm. for a period of 30minutes.

The dimensions of the specimen after impregnation were 21.5 mm. x 68.5mm. x 580.5 mm. It was subsequently kept in a heating chamber at 80 C.for 15 minutes. The piece of wood was then bent by hand through 180degrees with about 3 cm. bending radius. Drying was accomplished underbending pressure at 115 C. The specimen displayed no signs of fracture.The weight of the specimen was 497.1 g. prior to impregnation, 1004.5 g.after impregation and 467.1 g. after drying.

EXAMPLE 2 In this example the efl'ect of hydrazine on the compresibilityand hardness of specimens prepared from birch, alder and pine wood wasinvestigated. Impregnation was carried out as in the preceding example,using 15% aqueous solution of hydrazine. Pressing was accomplished in aconventional sodium press with 6 mm. pitch of the screw and 60 cm.length of the handle bars. The press was operated by hand. Thecompression time was 4 hours and compression temperature, 150 C. Tables1 'to 3 show the characteristics of birch, alder and pine wood beforeand after treatment. The hardnesses were measured perpendicular to thegrain.

TABLE 1.-BIRCH Compressed Untreated Impregnated and driedCharacteristics wood wood wood Thickness, mm 9. 7 W1 th, mm 44. 0Length, mm. 97. 0 Volume, em 3 41. 2 Weight, g 58. 5 Density, g./cm. 1.42 Hardness, B 2, 000

TABLE 2.ALDEB Compressed Untreated Impregneted and (his Charaet eristies wood wood wood Thickness, mm-.- 5. 9 45. 0 99. 5 26. 4 32. 4 1. 23 1,520

TABLE 3.PINE

' Compressed Untreated Impregnated and dried Characteristics wood woodwood Thickness, mm. 19. 8 20. 7 9. 3 Width, mm-.. 47. 9 50. 9 47. 1Length, mm.- 97. 6 97. 7 97. 5 Volume, cm 92.6 42.7 Weight, g 44. 1 73.8 41. 0 Density, gJcm)- 0. 47 0. 98 Hardness, B 790 It is seen from thetables that the greatest decrease in thickness and decrease of volumeoccurred in alder wood. The volumes were reduced, in the case of birch,alder and pine, by the respective amounts of 58.3, 70.2 and 59.3percent. The highest hardness was achieved with birch, and the lowestwith pine wood.

It has been found that the original density of the wood to be treatedhas an influence on its compressibility and increase in hardness. Withthe increasing original density, the compressibility and the hardnessachieved by treatment according to the invention both decrease.

EXAMPLE 3 In order to study the effect of concentration of the hydrazinesolution, pieces of birch wood of about 20 x 127 x 117.7 mm. size wereimpregnated with hydrazine solutions of various concentrations.impregnation, compression in the direction of thickness and drying werecarried out as in Example 2. For purposes of comparison the sameexperiment was also carried out, using for impregnating fluid merewater, and 25% ammonia. Table 4 shows the thickness, density andhardness of the specimens before and after treatment. The hardnesseswere measured perpendicular to the grain. The results reveal thathydrazine solution of about 5% concentration still exerts a notableeflect on the compressibility and hardness of wood.

TABLE 4 impregnated and pressure- Untreated wood dried woo Thiok- Den-Hard- Thick- Den- Hard.

ness, sity, ness, ness, sity, ness- Impregnating substance mm. g./cm. B.mm. gJem. B,

Hydrazine,15.4% 20.1 0. 52 200 7.0 1. 42 2,000 Hydrazine, 7.77 20.1 0.54200 3.2 1.20 1,800 Hydrazine, 5.1 20. 2 0. 60 200 9. 9 1. 11 Water 20.10.00 200 15.0 0.71 300 Ammonia, 26% 20.2 0. 68 200 12.3 1. 04 700EXAMPLE 4 TABLE 5 The wood specimens prepared in Example 2 were trans- 5Ultimate bending Young's modulus or f d f l b t ditio C -R HImpregnating substance strength, kgJem. e1ast1c1ty,kg./em. into 65%relative humidity (at 20 C.). The dimensi ns Hydrazine,15.4% 5,800452,000 of the spec1mens remained unchanged for 4 days. The ggggggggg? gggg igg fi weight of the specimens of alder wood increased by about 1%and that of the birch spec1mens by about 0.4%. The 20 What is claimedis:

volume of the pine specimens increased about 1.5% and their weight,about 3.7% In an experiment with identical, untreated pieces of wood theincrease in volume was about 3% for pine and 2.64% for birch. Theincrease in weight was 5.5% for pine and 4% for birch.

EXAMPLE 5 Birch veneers of 2.7 mm. thickness were impregnated withhydrazine solution and pressure-dried as in Example 2. The thickness ofthe veneers after drying was 1.3 mm. Tested by hand, the veneers had fargreater strength than conventional veneers of equivalent thickness. Thehardness had also considerably increased (1500' B.).

EXAMPLE 6 Bars (with 5.10 x 18.55 mm. cross section) made of birch woodtreated in accordance with Example 2 were tested for ultimate bendingstrength according to B.S.S. 373:1957. The hydrazine concentrationsemployed at impregnation were 15.4% and 7.7%. For comparison, theultimate bending strength was also determined for bars made of untreatedbirch wood (8.4 x 25.1 mm. cross section). The results are presented inTable 5, which also states the moduli of elasticity calculated for thetest bars.

1. A method of laminating and shaping wood veneers comprisingimpregnating at least one wood veneer with hydrazine, adhesively bondingsaid veneer to at least one surface of an untreated wooden board,whereupon the laminated product is formed into a desired shape usingheat and pressure.

2. A method of laminating and shaping wooden boards comprisingimpregnating at least two wooden boards with hydrazine, adhesivelybonding said boards to each other, whereupon the laminated product isformed into a desired shape using heat and pressure or pressure alone.

References Cited FOREIGN PATENTS 2,028,377 12/1970 West Germany 144-327ALFRED L. LEAVITI, Primary Examiner R. A. DAWSON, Assistant ExaminerU.S. Cl. XJR.

